1. Field of the Invention
The present invention relates to lamps, and in particular to an electric discharge lamp with a lamp body having an arc path formed therein.
2. Background Art
An electric discharge lamp is a lighting device comprising a transparent tube within which a gas is energized by an applied voltage and thereby made to glow. A fluorescent lamp is an electric discharge lamp that produces light by the fluorescence of a phosphor coating. A fluorescent lamp comprises a glass tube filled with a mixture of argon and mercury vapour. The glass tube in a fluorescent lamp can be straight or it can comprise a grid having a plurality of xe2x80x9cUxe2x80x9d shaped turns forming a serpentine pattern.
Metal electrodes at each end of the glass tube are coated with an alkaline-earth oxide that gives off electrons easily. When current flows through the ionized gas between the electrodes, it emits ultraviolet radiation. The inside of the tube is coated with phosphors, which are substances that absorb ultraviolet radiation and fluoresce (re-radiate the energy as visible light). Two common phosphors are zinc silicate and magnesium tungstate. A starter and ballast provide the extra voltage, up to four times of the operating voltage, needed to ionize the gas when starting.
Conventional Electric Discharge Lamps
The glass tubes in some prior art electric discharge lamps are quartz tubes which, as stated above, can be straight or serpentine shaped. An example of a serpentine shaped electric discharge lamp is shown in FIGS. 1A and 1B. In the flat type fluorescent lamp lighting device shown in FIG. 1B, the numerals 21 and 22 represent two transparent glass plates assembled and sealed by solder glass at the periphery thereof to form a lamp body. The transparent glass plate 22 has a groove 23 formed by a forming process at its facing surface against the glass plate 21. On the inner surface of the groove 23 is provided with a fluorescent film 24. The groove 23 forms a discharge channel 25 in a serpentine form extending over most of the surface area of the transparent glass plate 21. Discharge channel 25 is sealed and filled with mercury-vapor and an inert gas such as argon.
Both the ends of the discharge channel 25 have electrode leads 26A and 26B, one electrode lead provided at each end. An exhaust pipe 27 extending out from a part of the discharge channel is one whose tip is cut off after the completion of the processes of exhausting the air and filling in the gas. A reflecting layer 28 is formed by a film of metal, metallic oxide or resin which is coated or vapor-deposited on the non-luminous back side surface of the transparent glass plate 22.
A light transmission uniformity means in the form of a mask 29 is also formed by a film of metal, metallic oxide or resin which is coated or vapor-deposited on the luminous side surface of the transparent glass plate 21. The thickness or the area of the mask may partially be varied for the brightness distribution to be uniform at the luminous surface of the transparent glass plate 21. The reflecting layer 28 and the mask 29 are formed directly or integrally on the transparent glass plates 22 and 21, respectively, but it can be arranged that, instead of the reflecting layer 28 and the mask 29, a defuse plate or a reflecting plate may separately be placed one at the front side of the transparent glass plate 21 and the other at the back side of the transparent glass plate 22. Glass cover or reflector 30 forms a layer above the lamp body.
Difficulties in Forming the Arc Path
The serpentine discharge channel 25, shown in FIG. 1, defines a plurality of arc paths extending lengthwise across the transparent glass plate 21. The larger the number of turns in the serpentine form, the better will be the uniformity in the brightness distribution. Due to the physical limitations associated with current lamps, however, the number of turns that one can manufacture into serpentine discharge channel 25 is limited because the minimum thickness of the wall of the quartz tube used to construct serpentine discharge channel 25 is 1 millimeter. Therefore, at a minimum, 2 millimeters of glass are in between each parallel channel in the arc path of the lamp body.
In addition, structural limitations associated with a channel of bent glass further make the configuration of FIG. 1 disadvantageous. First, when forming a glass channel such as the one shown in FIG. 1, glass is gathered on the inside of the radius of each bend, for instance at locations 40 and 50. FIG. 1C provides an enlarged view of a prior art bend. Inside radius 40 is a thick wall of glass and illustrates where glass has gathered in the manufactured bend. When the glass is gathered at the bends as shown in FIG. 1C, it causes a non-uniformity of thickness in the bends of serpentine discharge channel 25. The non-uniformity of thickness causes the lamp to produce dark spots in these areas separating the arcs. Second, the outside of each bend becomes thin, for instance at locations 60 and 70, which makes the lamp body extremely fragile and prone to breaking. As shown in the expanded view of FIG. 1C, the outside radius 60 of the bend is much thinner than the inside radius 40 of the bend. What is needed is a lamp that has a rigid lamp body with arc paths that are extremely close together so it can provide a more uniform output of light.
The present invention provides an arc path formed in a lamp body. In accordance with one or more embodiments of the present invention, the lamp body has a plurality of closely spaced, parallel vanes which form the arc path. In one embodiment, the lamp body comprises a bottom and top plate, and a front and back sealing member. The bottom plate may be a flat plate, which may be made of quartz or other suitable glass material, that has a plurality of vanes machined into it out to its edges. Alternatively, the vanes may be separate from the bottom plate and sealed onto it. The top plate is sealed to the bottom plate. The front and back sealing members are sealed to the front and back ends of the plates to complete the seal of the lamp body.
In another embodiment, the bottom plate is a solid block. The block can be made of quartz or other suitable glass material, which has the vane pattern machined onto it stopping short of the edges. The solid block is then sealed at the top and outside edges by the top plate, without the need for front and back sealing members. In another embodiment, a solid block of quartz or other suitable glass material has holes drilled completely through it. The material left between the holes at the front and back ends forms a septum. Every other septum is machined back to provide clearance for the arc as it moves through the arc path and turns the corner at the end of each hole. The front and back ends are then sealed to complete the lamp body.
In one embodiment, the top and bottom plates are designed to emit differing wavelengths of light. This can be accomplished, for instance, by having the top plate be an ozone producing glass and the bottom plate being an ozone free glass. In another embodiment, the bottom plate is mirrored or has a highly reflective coating, which provides increased output from a single side of the lamp. In yet another embodiment, one side of the lamp can be focused on a single point using a plurality of lenses.
The vanes of the present invention allow for a much larger number of turns to be manufactured into the lamp body, which allows for a more even light distribution. Additionally, the vanes provide a structure to the lamp body that is more sturdy than was possible before.